Path: news.eternal-september.org!eternal-september.org!feeder3.eternal-september.org!panix!.POSTED.2602:f977:0:1::2!not-for-mail
From: Ted Heise <theise@panix.com>
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Charging from tow vehicle
Date: Sat, 8 Mar 2025 19:38:39 -0000 (UTC)
Organization: My own, such as it is
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Okay, I'm a dumbass.  I made up a table of the various cases I 
wanted to test, but when I got back from a couple of hours at the 
storage place and started writing up a summary I realized I had 
filled in the most critical combination with info that should have 
gone in a different row.  So I had to go back and test that last 
case.

Bottom line is the Acadia will in fact charge the LI battery 
installed on the Lance via the 7-pin connection, but with the 
fridge running the battery discharges.  See inline for more.



On Fri, 7 Mar 2025 11:48:30 -0600,
  sticks <wolverine01@charter.net> wrote:
>  On 3/7/2025 10:55 AM, Ted Heise wrote:
> > On Thu, 6 Mar 2025 17:56:09 -0600,
> >    sticks <wolverine01@charter.net> wrote:
> >>   On 3/6/2025 7:54 AM, Ted Heise wrote:

> >>> Pretty sure there is power going into the trailer too, 
> >>> because my memory (though not certain) is that the interior 
> >>> lights and other 12 V things work in the same circumstance 
> >>> (i.e., no battery connected, just the running TV).

I've confirmed that the Lance's 12 V system is powered when 
connected only to the running Acadia via the 7-pin cord (i.e., 
without the LI battery connected).  As expected, the 120 V system 
in the Lance does not have power in this case.


> > I think that [PD 4000's limitation] is probably correct.  
> > Here is the (typical) exterior wiring diagram from the 
> > manual...
> > 
> > https://panix.com/~theise/wp-content/uploads/2025/03/Lance-1475-ext-wiring-traced.pdf
> > 
> > This shows that the 7-pin does connect to the battery, and seems
> > consistent with the trailer manual statement that "Normally the
> > battery will be kept charged by either the tow vehicle charging
> > system while on the road or by the AC/DC power convertor when
> > plugged into AC service."

>  Your pic show about the same thing I found out today.  First, I 
>  got two pics from the manual and the first from page 50 does 
>  state the power prong on the 7 prong plug goes to the battery 
>  and will provide charge.
> 
> <https://postimg.cc/gallery/r4xVRjj>
> 
>  The second pic is similar to your showing the PD4000 as well as 
>  the 7 prong.  It has a smallest size of 8 gauge right at the 
>  generator and has a capability of 35 amps, though it has a 30 
>  amp inline mini breaker. This would be a nice setting for 
>  charging the Lithium and probably close to what you'd get if 
>  you did a DC to DC generator at either 20 or 30 amp.
> 
>  I would agree this setup is not really taking into 
>  consideration having a lithium battery, though I don't think ti 
>  hurts anything if you leave it as is and go ahead and install a 
>  DC to DC converter.  It is just a trickle going to that.

I looked at quite a variety of things, but the gist of it is that 
voltage at the LI battery when connected to the running Acadia 
mirrors that on the Acadia's dash gauge: in the vicinity of 13.4 
to 14.0 V.  The LI battery app shows that it's getting about 2 A 
from the Acadia.  If my rough calculations are correct, 6 hours of 
towing would add back about 12 Ah, so the charging at this rate is 
not going to be fast.

FWIW, the LI battery app showed 0.6 hours to full charge at the 2 
A rate when it was 98/99% full.
 

> >>   So you do have some AC outlets in the unit I believe, and 
> >>   these most likely only work when the shore line cord is 
> >>   plugged in. There might be a disconnect switch somewhere, 
> >>   but it probably just has a bank, or something like a 
> >>   electrical box that ties in all the AC outlets to the 
> >>   shoreline somehow.
> > 
> > Yes, correct, there are AC outlets in the Lance.  Looks like 
> > the power goes from the shore line to the outlets by way of 
> > the load center...
> > 
> > https://panix.com/~theise/wp-content/uploads/2025/02/Lance-schematic.jpg
> 
>  Yep.  You plug in your shore cord, you will get power at the AC 
>  outlets. Since you have no inverter, these should be dead 
>  unless you plug in the shore line.

Correct, no juice at the 110 V outlets when on the Acadia and/or 
the LI battery.

Interestingly, I noticed an old cigarette lighter plug-in on an 
interior wall receptacle along with a 5 V USB jack.  I'm guessing 
that would provide 12 V.


> > So the diagram I posted shows the power does go from the 
> > Acadia to the Lance battery.  Is that a problem?  I don't 
> > think there's any other kind of control box, unless it's in 
> > the junction box under the Lance tongue (or maybe in the 
> > Acadia's tow system).
> 
>  You could ask the dealer if this can be left alone if you add a 
>  DC to DC converter, or even if they think it will harm the 
>  alternator on the Acadia, but I don't think it would matter and 
>  could just be left alone.

I think this is right.  The low power over the 7-pin is pretty 
unlikely to ever get the LI battery up to full, unless it's very 
close before starting a day of towing.

I also tested the system with the fridge running.  With only the 
LI battery connected, its app showed the fridge was drawing about 
17 amps and that it would be discharged in under 6 hours.  With 
the running Acadia also connected, the LI battery app showed a bit 
over 7 A draw, with somewhat over 14 hours of runtime left.

From this, I take that the fridge draws so much that it robs from 
the LI battery as well as from the Acadia.  My impression is that 
if the LI battery is relatively full at the start of a towing day 
I should just disconnect it while towing so it doesn't get drawn 
down and it's SOC is preserved.  The fridge should run okay on 
only the jiuce from the Acadia via the 7-pin.

on the other hand, if the LI is low on charge when I start a day 
of towing, I could consider leaving it connected and running the 
fridge on propane.


> >>> mind, I seemed to recall the Acadia had a 110 V outlet in 
> >>> the second row of seats.  Indeed there is when I checked it 
> >>> this morning.  Rated at 150 W max, it seems I could use this 
> >>> with my NOCO GENIUS 5 charger (max 75 W draw) to charge the 
> >>> trailer battery in a pinch. Might could even use it to run 
> >>> the coffee grinder.  ;)
> >>
> >>   It looks like this unit is more for non-lithium batteries, 
> >>   but it does say it can charge them.  I'm not sure, though. 
> >>   Doesn't seem to have enough power capability to do much of 
> >>   anything.

So to recap, I'm now thinking the Acadia can charge the LI 
battery, albeit on the slow side.


> >>> Gotta run to see the cardiologist now, but will come back to 
> >>> this later today.
> >>
> >>   Hope you got some good reports!
> > 
> > Thanks!  Just sporadic supraventricular arrhythmias, not a 
> > fib. Pretty benign according to the cardiologist.
> 
>  Good to know.  Keep the rubber down!

Thanks!  The temps here are approaching 50 F and the wind is light 
(for here), so I'm gonna head out on the bike shortly.  Will do my 
best to keep the rubber down!

-- 
Ted Heise      <theise@panix.com>       West Lafayette, IN, USA